Switch contact



R- B. HUNTER SWITCH CONTACT Filed July 23, 19

H I 34 Z6 3 34 33 5 pril 9, 1940.

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' UNITED STATES PATENT OFFICE? I SWITCH CONTACT' Richard B. Hunter,Shorewood, Wis., assignor to Cutler-Hammer, Inc., Milwaukee Wia, a

corporation of Delaware Application July 23, 1937, Serial No. 155,212

2 Claims. (01. 200-171) This invention relates to switch contacts andmore particularly to contacts of the type employed in connection withdrum controllers, although it late be understood thatcontacts of thecharacter herein disclosed may be employed I in other electricaldevices.

' aforementionedcharacter which is positively held against rotarymovement with respect to the finger to which it is secured.

Another object is to provide a contact tip of the aforementionedcharacter having an embedded securing element, wherein the embeddedportion of the securing element is sufflciently removed from the contactsurface of the tip to provide an adequate amount of wear allowance.

Another object s to provide a contact tip in which the securing elementis rigidly held and supported in a novel and efi'ective manner.

.Another object is to provide a readily removable and replaceablecontact tip which is simple in construction and which can be producedeconomically. v

Other objects and advantages of the invention will hereinafter appear.

Various forms of contact tips have heretofore been proposed, whichindividually possess certain advantages which are of vvalue dependingupon their application. Those contact tips which are adapted to bepermanently'secured to contact fingers, as by riveting, are satisfactoryfor use in drum controllers, for instance, which are employed in suchrelatively light service that wear and burning of the contact tips'isnegligible.

- However, controllers which are employed for relatively heavydutyservice, such as requires fre quent commutation of circuits carryingheavy currents, and in which high contact pressures are required,necessitate frequent replacement of the contact tips dueto'relatively-rapld wear'and burning thereof. It is obvious that apermanently secured contact tip is undesirable where frequentreplacement is necessary, and in recognition of the need for an easilyremovable and attachable contact tip various forms thereof haveheretofore been proposed.

In drum controllers the engagement of the contact tip with thecooperatingcontacts carried by the rotary drum is Preferably effectedwith a maximum width of the contacting areas, and accordingly anecessary feature of such a tip is to provide means whereby the same isnon-rotatably held with respect to the contact finger. Such means,heretofore proposed, include such devices 5 asan abutment formed at oneend of the contact tip to cooperate with the outer end of the finger,the abutment however, preventing reversible attachment of the tip. Othertips are formed with recesses requiring specially formed projection 10on the contact finger, or a separate element carried by the finger andhaving a projection to cooperate with a recess or recesses in the tip.

The present invention provides the aforementioned feature ofnon-rotatable securement in a novel manner and other desirable featuresas set forth in the foregoing objects, and the advantages of suchfeatures will be apparent from the following description with referenceto the single embodiment of the invention illustrated, in theaccompanying drawing; it-belng understood that the embodimentillustrated is susceptible of modification in respect of certain detailsof construction thereof without departing from the scope of the appendedclaims.

Inv the drawing, Figure l is a side elevational view, with parts thereofshown in vertical section, of a contact finger having secured thereto aform of contact tip embodying my invention;

Fig. 2 is a top plan view of the contact finger shown in Fig. l;

Fig. 3 is a perspective view, in separated relation, of the improvedcontact tip shown in Fig. 1 and the outer end .portion of the contactfinger, showing a preferred form of the latter and indicating themanner-of cooperation of the parts; and. i

Fig. 4 is a plan view of the contact tip.

Referring now more particularly to Fig. 1 of the drawing, the numeraldesignates a segmental contact mounted on a. rotary drum in a positionto engage the contact tip 2 secured to the outer endportion of acontactfinger I. The romember 5 formed of suitable insulating material.as

' Contact finger 3 is secured to supporting rod 4 by clamping meanscomprising a clamping member 3 having arms 1 and 3 formed at arightangle to each other to engage two sides of the rod 4. Ann I alsoforms a supporting base plate for the contact mechanism. Cooperatingwith clamping member 8 is a second clamping member 3 having arms l0 andIi formed at a right-angle to each other to engage the other two sidesof rod 4. The clamping members 6 and 3 are firmly held in clampingengagement with supporting rod 4 by b0lts,i2 and i3 and nuts l4.

Contact finger 3 is provided adjacent to the inner end thereof with anopening to freely receive the reduced portion of bolt l2. A coiledcompression spring I! encircles portion 15 and is held under compressionbetween the outer surface of contact finger 3 and theinner surface of acup washer I? which is retained on portion l5 by a cotter pin i8. Theextreme inner end of contact finger 3 is bent downwardly and is formedin a manner to provide a bearing edge or surface i3 which seats within aSaddle or open bearing formed on the outer face of arm I of clampingmember 6.

One end portion of a flexible conductor or pigtail 2! is secured to theinner end portion of contact finger 3, the other end of said conductorbeing secured on bolt l3 between nuts l4 and 22 together with a solderlug 23 of well known form.

Associated with contact finger 3 is a contact pressure adjusting devicecomprising a polygonal headed screw 24 the shank of which is threadedinto a tapped opening in the contact finger and is adapted in theinactive position of said finger to engage the upwardly offset extension25 of arm I. Adjustment of screw 24 effects variation of the initialposition of contact tip 2 and provides for correct inactive positioningof tip 2 as the latter wears down. A reflexed or substantially U-shapedspring element 26 is provided with an upwardly bent fiat projection 21which-is adapted to yieldably engage any one of the fiat sides of thehead of screw 24 to effect retention of the latter in any adjustedposition against displacement by vibration. One of the legs of springelement 26 engages the outer surface of contact finger 3 while the otherleg engages the inner surface of the head of screw 24, said legs havingarmed, relatively large openings to freely receive the shank of screw 24and to provide a degree of longitudinal movement of spring element 26 topermit adjustment of screw 24.

When the rotary drum is of sufficiently large diameter to presen thedanger of arcing between the segmental contacts carried thereby and themetal clamping members of the contact mechanism supporting means, ashield 23 formed of suitable insulating material is preferably mountedon the extension 29 of clamping member 9 by a screw 30, as shown in Fig.1.

The contact tip 2 comprises essentially a suitably shaped body of metal,preferably copper, having embedded therein the head 3i and a .portion ofthe threaded shankof a securing element or stud 32, which is preferablymade of steel. The stud and the contact tip are assembled in a wellknown manner;the head 3| being inserted in a recess in the tip formed toreceive it and the metal then pressed or flowed and shaped around it asby swaging or hot forging of the copper to positively lock the stud inposition in the tip. ,The stud head 3| is illustrated in the drawing asbeing of fiat circular form, the peboss or projection 34 formed on saidsurface.

Projection 34 is adapted to be accommodated within an elongated openingformed in the forward end of contact finger 3, the walls of said openingclosely engaging the periphery of said projection to positively andnon-rotatably interlock the contact tip with said finger. By means of anut 35 which is threaded on stud 32 and a.

lock washer 31 which is interposed between said nut and the uppersurface of contact finger 3, the contact tip 2 is rigidly secured tosaid contact finger.

As best shown in Fig. 4 the width of the projection 34 correspondssubstantially with the diameter of stud 32, this width being preferredto a lesser width to avoid specially forming the opening 35 toaccommodate the shank of stud 32. Moreover, the width of projection 34should be sufficient to present a relatively large peripheral wallsurface for cooperative engagement with the walls of opening35 and alsoto provide an adequate body of metal to prevent shearing of theprojection by a wall of said opening when the nut 36 is turned totighten the tip in position. On the other hand, a projectionsubstantially larger than that shown is objectionable as it wouldrequire an opening 35 of such size as to materially weaken the contactfinger.

It should be noted that the projection 34 is preferably arrangedlongitudinally with respect to the body of the contact tip 2, that is,in line with the direction of movement of the segmental contacts of thedrum, and that the opening 35 is likewise preferably arrangedlongitudinally with respect to the contact finger 3. By this arrangementthe shank of stud 32- is well supported by projection 34 in thedirection of thrust, whether the drum is being rotated in one directionor the other.

The advantages of the aforedescribed arrangement are particularlyevident when it is pointed out that if the projection 34 were arrangedtransversely of the contact tip the desired support for the shank ofstud 32 in the direction of thrust would not be provided unless theprojection were made substantially wider; and further, if the opening 35were arranged transversely with respect to contact finger 3, the latterwould be materially weakened unless it in turn were made wider toaccommodate an opening so arranged. However, it iausnally desired tomake drum controllers of as small size as is practically possible toconserve materials and reduce the cost thereof, and obviously if thecontact fingers were required to be made wider than is necessary toserve their purpose, the center-to-center spacing of the fin-- gerswould be greater, thus materially increasing the size of the drumcontroller. I

The character and arrangement of projection 34 serves a further andimportant purpose. In

order to obtain the maximum amount of wear from the contact tip the studhead 3| should be embedded in the tip as far removed from the contactsurface as possible. As best shown in Fig. 1 the projection 34 providesan added thickness of metal enabling the head II to be located dad insaid body of relatively soft metal closely relatively close to thesurface 33 of the contact tip 2 without danger of the stresses incurredduring tightening of nut 32 or the stresses incident to operation of thedrum resulting in displacement of the stud from its embedded position.What I claim as new and desire to secure by Letters Patent is:

1. A contact tip comprising an integral body of relatively soft metalhaving surfaces for engagement with 'a cooperating contact and forengagement with a supporting finger, and having on the latter surfacefor interlock with such supporting finger a projection which isrelatively low and of elongated form with parallel fiat sides,

and further comprising a securing-member hav-- ing a threaded shankterminating in a relatively thin wide head, such securing member beingof relatively hard metal and having its head embedadjacent the fingerengaging surface of said body for preservation of depth of the portionof said body subjected to. wear and said projection on the fingerengaging surface of said body being formed to overlie the head of saidsecuring meming a flat surface for engagement with saidsupportingmember, the contact tip having a projection formed on said fiat surface,said projection being adapted for interlocking non-rotatable andnon-slidable engagement with the walls of said opening, and a-securingelement of a relatively harder metal having a head embedded in said tipclosely adjacent to said flat surface to provide a wearing portion ofmaximum depth and having a threaded shank extending exteriorly of saidtip substantially through the center of said projection, said elementbeing adapted to assist in providing for securement of said tip to saidsupporting member. l

RICHARD B. mm.

